Light olefins serve as feeds for the production of numerous chemicals and have traditionally been produced through the process of steam or catalytic cracking. However, due to the limited availability and high cost of petroleum sources, the cost of producing light olefins from such petroleum sources has been steadily increasing.
The search for alternative materials for light olefin production has led to the use of oxygenates such as alcohols and, more particularly, to the use of methanol, ethanol, and higher alcohols or their derivatives. Molecular sieves such as microporous crystalline zeolite and non-zeolitic catalysts, particularly silicoaluminophosphates (SAPO), are known to promote the conversion of oxygenates to hydrocarbon mixtures in a reactor. Numerous patents describe this process for various types of these catalysts: U.S. Pat. Nos. 3,928,483; 4,025,575; 4,052,479; 4,496,786; 4,547,616; 4,677,242; 4,843,183; 4,499,314; 4,447,669; 5,095,163; 5,191,141; 5,126,308; 4,973,792; 4,861,938; 7,309,679; and 9,643,897.
When a catalyst is exposed to oxygenates, such as methanol, to promote the reaction to olefins, carbonaceous material (coke) is generated and deposited on the catalyst. Accumulation of coke deposits interferes with the catalyst's ability to promote the reaction. As the amount of coke deposit increases, the catalyst loses activity and less of the feedstock is converted to the desired olefin product. The step of regeneration removes the coke from the spent catalyst by combustion with oxygen, restoring the catalytic activity of the catalyst. The regenerated catalyst may then be exposed again to oxygenates to promote the conversion to olefins.
Recently, it has been shown that partial regeneration of spent catalyst provides a selectivity advantage in a methanol to olefin (MTO) conversion process. Thus, it is believed that the amount of coke on regenerated catalyst can be adjusted to maximize light olefin yields based on various reactor condition.
Partial regeneration of MTO catalyst introduces challenges for control of the extent of regeneration. Fluidized bed regeneration requires a specific range of superficial velocity to achieve sufficient gas-solid contacting and recovery of entrained fines from the flue gas. Consequently, once a regenerator is designed, the amount of air supplied to the regenerator can only be controlled in a small range. Therefore, there is a need for processes which control the extent of regeneration of the catalyst to achieve the desired coke on the regenerated catalyst.